1. Field of the Invention
The present invention relates generally to rupture disk apparatus and manufacturing methods, and more particularly, to rupture disks, assemblies, and manufacturing methods wherein the rupture disks have an area or areas of weakness to facilitate opening of the disk.
2. Description of the Prior Art
A great many pressure relief devices of the rupture disk type have been developed and used. Generally, such devices include a rupture disk supported between a pair of support members or flanges, which are in turn connected to a relief connection in a vessel or system containing pressurized fluid. When the pressurized fluid within the vessel or system exceeds the design rupture pressure of the rupture disk, the disk ruptures causing pressurized fluid to be relieved from the vessel or system.
Rupture disks fall into the general categories of forward acting tension type disks and reverse acting disks. Certain forward acting tension type disks have been developed using a score line in the surface of the disk to ensure opening at a specific area. More recently, reverse buckling rupture disks have also included scores formed on a surface to define an area or areas of weakness such that upon reversal, the disk tears in such area or areas of weakness. Scored reverse buckling rupture disk manufacturing methods are described in U.S. Pat. No. 4,441,350 to Short et al. issued on Apr. 10, 1984 and U.S. Pat. No. 4,458,516 issued to Naumann on Jul. 10, 1984.
While scored reverse buckling rupture disks have been used successfully and have obviated the need for knife blades in a number of applications, fragmentation and/or tearing away of portions of the disks can still be a problem. That is, upon the reversal and rupture of the scored reverse buckling rupture disk in the area or areas of weakness defined by the scores, fragmentation and tearing away of parts from the disk can occur. These same fragmentation and tearing away problems may also occur in tension loaded rupture disks.
To reduce the chances of fragmentation upon rupture, C-scored techniques have been developed. Such disks include, but are not limited to, an area or areas of weakness formed by one or more scores which define a circular or similar blow-out portion hinged to the reminder of the disk by an unweakened hinge area. Also, with respect to reverse acting disks, rupture disk assemblies have been developed that include a support member to contact the disk as it reverses and thereby lessen the chance of tearing away. For example, U.S. Pat. No. 5,167,337 to Short et al. issued Dec. 1, 1992 describes a C-scored reverse buckling rupture disk assembly that includes an inwardly extending support member for preventing the blow-out portion of the disk from fragmenting or tearing away at the hinge upon rupture.
A general problem in the manufacture of scored rupture disks that has continued to exist is that the tooling used to form the scores can be and often is damaged when the disk material is scored too deeply. For example, score dies of the type described U.S. Pat. Nos. 4,441,350 and 4,458,516 cited above can be and often are collided together which dulls or breaks the score blades requiring their repair or replacement. Yet another problem with conventional scoring techniques is that the material directly under the score blade becomes work hardened such that it may be difficult to score the disk to a desired thinness.
Another problem that has existed in scored rupture disks prior to the present invention is the premature failure of the disks due to pressure cycling. Pressure cycling occurs in many rupture disk applications and includes positive pressure variations, as well as going from a positive to a negative pressure. Fluctuation in the pressure of the pressurized fluid exerted on the rupture disks may cause them to flex, which in turn may cause the material forming the disks to fatigue and fail at the score or scores in the disks. This in turn results in the development of leaks and/or the premature failure of the disks. The industry has attempted to minimize-this fatiguing problem by supporting the scored region with, for example, the rupture disk head. However, this approach has not completely relieved the problem.
Thus, there is a continuing need for improved rupture disks, assemblies and methods which obviate the above mentioned problems.